Power generation system having compressor creating excess air flow and turbo-expander to increase turbine exhaust gas mass flow

ABSTRACT

A power generation system may include: a first gas turbine system including a first turbine component, a first integral compressor and a first combustor to which air from the first integral compressor and fuel are supplied. The first integral compressor has a flow capacity greater than an intake capacity of the first combustor and/or the first turbine component, creating an excess air flow. A second gas turbine system may include similar components to the first except but without excess capacity in its compressor. A turbo-expander may be operatively coupled to the second gas turbine system. Control valves may control flow of the excess air flow from the first gas turbine system to at least one of the second gas turbine system and the turbo-expander, and flow of a discharge of the turbo-expander to an exhaust of at least one of the first turbine component and the second turbine component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending US application numbers:application Ser. No. 14/662,760, application Ser. No. 14/662,770,application Ser. No. 14/662,780, application Ser. No. 14/662,785,application Ser. No. 14/662,796, application Ser. No. 14/662,800,application Ser. No. 14/662,803, all filed on Mar. 19, 2015.

BACKGROUND OF THE INVENTION

The disclosure relates generally to power generation systems, and moreparticularly, to a power generation system including a gas turbinesystem having a compressor creating an excess air flow and aturbo-expander to augment generator output and increase turbine exhaustgas mass flow of another gas turbine system, which turbine exhaust(s)may be used in one or more steam generators.

Power generation systems oftentimes employ one or more gas turbinesystems, which may be coupled with one or more steam turbine systems, togenerate power. A gas turbine system may include a multi-stage axialflow compressor having a rotating shaft. Air enters the inlet of thecompressor and is compressed by the compressor blade stages and then isdischarged to a combustor where fuel, such as natural gas, is burned toprovide a high energy combustion gas flow to drive a turbine component.In the turbine component, the energy of the hot gases is converted intowork, some of which may be used to drive the integral compressor througha rotating shaft, with the remainder available for useful work to drivea load such as a generator via a rotating shaft (e.g., an extension ofthe rotating shaft) for producing electricity. A number of gas turbinesystems may be employed in parallel within a power generation system. Ina combined cycle system, one or more steam turbine systems may also beemployed with the gas turbine system(s). In this setting, a hot exhaustgas from the gas turbine system(s) is fed to one or more heat recoverysteam generators (HRSG) to create steam, which is then fed to a steamturbine component having a separate or integral rotating shaft with thegas turbine system(s). In any event, the energy of the steam isconverted into work, which can be employed to drive a load such as agenerator for producing electricity.

When a power generation system is created, its parts are configured towork together to provide a system having a desired power output. Theability to increase power output on demand and/or maintain power outputunder challenging environmental settings is a continuous challenge inthe industry. For example, on hot days, the electric consumption isincreased, thus increasing power generation demand. Another challenge ofhot days is that as temperature increases, compressor flow decreases,which results in decreased generator output. One approach to increasepower output (or maintain power output, e.g., on hot days) is to addcomponents to the power generation system that can increase air flow tothe combustor of the gas turbine system(s). One approach to increase airflow is adding a storage vessel to feed the gas turbine combustor. Thisparticular approach, however, typically requires a separate power sourcefor the storage vessel, which is not efficient.

Another approach to increasing air flow is to upgrade the compressor.Currently, compressors have been improved such that their flow capacityis higher than their predecessor compressors. These new, higher capacitycompressors are typically manufactured to either accommodate new,similarly configured combustors, or older combustors capable of handlingthe increased capacity. A challenge to upgrading older gas turbinesystems to employ the newer, higher capacity compressors is that thereis currently no mechanism to employ the higher capacity compressors withsystems that cannot handle the increased capacity without upgradingother expensive parts of the system. Other parts that oftentimes need tobe upgraded simultaneously with a compressor upgrade include but are notlimited to the combustor, gas turbine component, generator, transformer,switchgear, HRSG, steam turbine component, steam turbine control valves,etc. Consequently, even though a compressor upgrade may be theoreticallyadvisable, the added costs of upgrading other parts renders the upgradeill-advised due to the additional expense.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a power generation systemincluding a first gas turbine system including a first turbinecomponent, a first integral compressor and a first combustor to whichair from the first integral compressor and fuel are supplied, the firstcombustor arranged to supply hot combustion gases to the first turbinecomponent, and the first integral compressor having a flow capacitygreater than an intake capacity of at least one of the first combustorand the first turbine component, creating an excess air flow; a secondgas turbine system including a second turbine component, a secondcompressor and a second combustor to which air from the secondcompressor and fuel are supplied, the second combustor arranged tosupply hot combustion gases to the second turbine component; aturbo-expander operatively coupled to the second gas turbine system; afirst control valve system controlling flow of the excess air flow alongan excess air flow path from the first gas turbine system to at leastone of the second gas turbine system and the turbo-expander; and asecond control valve controlling flow of a discharge of theturbo-expander to an exhaust of at least one of the first turbinecomponent and the second turbine component.

A second aspect of the disclosure provides a power generation system,comprising: a first gas turbine system including a first turbinecomponent, a first integral compressor and a first combustor to whichair from the first integral compressor and fuel are supplied, the firstcombustor arranged to supply hot combustion gases to the first turbinecomponent, and the first integral compressor having a flow capacitygreater than an intake capacity of at least one of the first combustorand the first turbine component, creating an excess air flow; a secondgas turbine system including a second turbine component, a secondcompressor and a second combustor to which air from the secondcompressor and fuel are supplied, the second combustor arranged tosupply hot combustion gases to the second turbine component; aturbo-expander operatively coupled to the second gas turbine system; afirst control valve system controlling flow of the excess air flow alongan excess air flow path from the first gas turbine system to at leastone of the second gas turbine system and the turbo-expander; and asecond control valve controlling flow of a discharge of theturbo-expander to an exhaust of at least one of the first turbinecomponent and the second turbine component, wherein the second controlvalve system includes a first control valve controlling a first portionof the discharge of the turbo-expander to an exhaust of the firstturbine component and a second control valve controlling a secondportion of the discharge of the turbo-expander to an exhaust of thesecond turbine component, wherein the second gas turbine system furtherincludes a rotating shaft coupling the second compressor, the secondturbine component, a starter motor and the turbo-expander.

A third aspect of the disclosure provides a method comprising:extracting an excess air flow from a first integral compressor of afirst gas turbine system including a first turbine component, the firstintegral compressor and a first combustor to which air from the firstintegral compressor and fuel are supplied, the first integral compressorhaving a flow capacity greater than an intake capacity of at least oneof the first combustor and the first turbine component; directing theexcess air flow along an excess air flow path to at least one of: asecond gas turbine system including a second turbine component, a secondcompressor and a second combustor to which air from the secondcompressor and fuel are supplied, the second combustor arranged tosupply hot combustion gases to the second turbine component, and aturbo-expander operatively coupled to the second gas turbine system; anddirecting flow of a discharge of the turbo-expander to an exhaust of atleast one of the first turbine component and the second turbinecomponent.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawing that depicts various embodiments of the disclosure, in which:

FIG. 1 shows a schematic diagram of a power generation system accordingto embodiments of the invention.

It is noted that the drawing of the disclosure is not to scale. Thedrawing is intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawing, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the disclosure provides a power generation systemincluding a gas turbine system including a compressor that creates anexcess air flow. Embodiments of the invention provide ways to employ theexcess air flow to improve output of the power generation system.

Referring to FIG. 1, a schematic diagram of a power generation system100 according to embodiments of the invention is provided. System 100includes a first gas turbine system 102. First gas turbine system 102may include, among other components, a first turbine component 104, afirst integral compressor 106 and a first combustor 108. As used herein,first “integral” compressor 106 is so termed as compressor 106 andturbine component 104 may be integrally coupled together by, inter alia,a common compressor/turbine rotating shaft 110 (sometimes referred to asrotor 110). This structure is in contrast to many compressors that areseparately powered, and not integral with turbine component 104.

Combustor 108 may include any now known or later developed combustorsystem generally including a combustion region and a fuel nozzleassembly. Combustor 108 may take the form of an annular combustionsystem, or a can-annular combustion system (as is illustrated in theFIGURES). In operation, air from first integral compressor 106 and afuel, such as natural gas, are supplied to combustor 108. Diluents mayalso be optionally delivered to combustor 108 in any now known or laterdeveloped fashion. Air drawn by first integral compressor 106 may bepassed through any now known or later developed inlet filter housing120. As understood, combustor 108 is arranged to supply hot combustiongases to first turbine component 104 by combustion of the fuel and airmixture. In turbine component 104, the energy of the hot combustiongases is converted into work, some of which may be used to drivecompressor 106 through rotating shaft 110, with the remainder availablefor useful work to drive a load such as, but not limited to, a generator122 for producing electricity, and/or another turbine via rotating shaft110 (an extension of rotating shaft 110). A starter motor 112 such asbut not limited to a conventional starter motor or a load commutatedinverter (LCI) motor (shown) may also be coupled to rotating shaft 110for starting purposes of first gas turbine system 102. Turbine component104 may include any now known or later developed turbine for convertinga hot combustion gas flow into work by way of rotating shaft 110.

In one embodiment, gas turbine system 102 may include a model MS7001FB,sometimes referred to as a 7FB engine, commercially available fromGeneral Electric Company, Greenville, S.C. The present invention,however, is not limited to any one particular gas turbine system and maybe implemented in connection with other systems including, for example,the MS7001FA (7FA) and MS9001FA (9FA) models of General ElectricCompany.

In contrast to conventional gas turbine system models, first integralcompressor 106 has a flow capacity greater than an intake capacity ofturbine component 104 and/or first combustor 108. That is, compressor106 is an upgraded compressor compared to a compressor configured tomatch combustor 108 and turbine component 104. As used herein,“capacity” indicates a flow rate capacity. For example, an initialcompressor of gas turbine system 102 may have a maximum flow ratecapacity of about 487 kilogram/second (kg/s) (1,075 pound-mass/second(lbm/s)) and turbine component 104 may have a substantially equalmaximum flow capacity, i.e., around 487 kg/s. Here, however, compressor108 has replaced the initial compressor and may have an increasedmaximum flow capacity of, for example, about 544 kg/s (1,200 lbm/s),while turbine component 104 continues to have a maximum flow capacityof, e.g., around 487 kg/s. (Where necessary, starter motor 112 may alsohave been upgraded, e.g., to an LCI drive motor as illustrated, toaccommodate increased power requirements for startup of first integralcompressor 106). Consequently, turbine component 104 cannot takeadvantage of all of the capacity of compressor 106, and an excess airflow 200 is created by compressor 106 above a maximum capacity ofturbine component 104. Similarly, the flow capacity of integralcompressor 106 may exceed the maximum intake capacity of combustor 108.In a similar fashion, the power output of turbine component 104 ifexposed to the full flow capacity of integral compressor 106 couldexceed a maximum allowed input for generator 122. While particularillustrative flow rate values have been described herein, it isemphasized that the flow rate capacities may vary widely depending onthe gas turbine system and the new, high capacity integral compressor106 employed. As will be described herein, the present inventionprovides various embodiments for power generation system 100 to employthe excess air flow in other parts of power generation system 100.

In the embodiment shown in FIG. 1, power generation system 100 alsoincludes one or more second gas turbine system(s) 140. Each second gasturbine system 140 may include a second turbine component 144, a secondcompressor 146 and a second combustor 148. Each second gas turbinesystem 140 may be substantially similar to first gas turbine system 102except compressor 146 thereof has not been upgraded or replaced andcontinues to have a flow capacity configured to match that of itsrespective turbine component 144 and/or combustor 148. As describedherein relative to first integral compressor 106, air from secondcompressor 146 is supplied to second combustor 148 along with a fuel,and second combustor 148 is arranged to supply hot combustion gases tosecond turbine component 144. Diluents may also be optionally deliveredto second combustor 148 in any now known or later developed fashion. Airdrawn by second compressor 146 may be passed through any now known orlater developed inlet filter housing 150. In second turbine component144, the energy of the hot combustion gases is converted into work, someof which is used to drive compressor 146 through rotating shaft 152,with the remainder available for useful work to drive a load such as,but not limited to, a generator 154 for producing electricity, and/oranother turbine via rotating shaft 152 (an extension of rotating shaft152). A starter motor 156 for start up operations relative to second gasturbine system 140 may also be coupled to rotating shaft 152.

Second turbine component 144 may also include one or more turbine nozzlecooling inlet(s) 158. As understood in the art, a stationary nozzle in aturbine component may include a number of inlets (not shown) for acooling fluid flow to be injected for cooling, among other things, thenozzles of the turbine component. Passages within and about the nozzlesdirect the cooling fluid where necessary. Although only one inlet isshown at a first stage of turbine component 144 for clarity, it isunderstood that each stage of turbine component 144 may include one ormore inlets, e.g., circumferentially spaced about the turbine component.In addition, although turbine nozzle cooling inlet 158 is illustrated asentering at or near a first stage of second turbine component 144, asunderstood, inlet(s) may be provided at practically any stage.

As also shown in FIG. 1, in one embodiment, power generation system 100may optionally take the form of a combined cycle power plant thatincludes a steam turbine system 160. Steam turbine system 160 mayinclude any now known or later developed steam turbine arrangement. Inthe example shown, high pressure (HP), intermediate pressure (IP) andlow pressure (LP) sections are illustrated; however, not all arenecessary in all instances. As known in the art, in operation, steamenters an inlet of the steam turbine section(s) and is channeled throughstationary vanes, which direct the steam downstream against bladescoupled to a rotating shaft 162 (rotor). The steam may pass through theremaining stages imparting a force on the blades causing rotating shaft162 to rotate. At least one end of rotating shaft 162 may be attached toa load or machinery such as, but not limited to, a generator 166, and/oranother turbine, e.g., one of gas turbines 102, 140. Steam for steamturbine system 160 may be generated by one or more steam generators 168,170, i.e., heat recovery steam generators (HRSGs). HRSG 168 may becoupled to an exhaust 172 of first turbine system 102, and HSRG 170 maybe coupled to an exhaust 174 of second turbine system(s) 140. That is,exhaust 172, 174 of gas turbine system 102 and/or gas turbine system(s)104, respectively, may be supplied to at least one HRSG 168, 170 forpowering steam turbine system 160. Each gas turbine system may becoupled to a dedicated HRSG, or some systems may share an HRSG. In thelatter case, although two HRSGs 168, 170 are illustrated, only one maybe provided and both exhausts 172, 174 directed thereto. After passingthrough steam generators 168, 170, the combustion gas flow, now depletedof heat, may be exhausted via any now known or later developed emissionscontrol systems 178, e.g., stacks, selective catalytic reduction (SCR)units, nitrous oxide filters, etc. While FIG. 1 shows a combined cycleembodiment, it is emphasized that steam turbine system 160 includingsteam generators 168, 170 may be omitted. In this latter case, exhaust172, 174 would be passed directly to emission control systems 180 orused in other processes.

Power generation system 100 may also include any now known or laterdeveloped control system 180 for controlling the various componentsthereof. Although shown apart from the components, it is understood thatcontrol system 180 is electrically coupled to all of the components andtheir respective controllable features, e.g., valves, pumps, motors,sensors, gearing, electric grid, generator controls, etc.

Returning to details of first gas turbine system 102, as noted herein,first integral compressor 106 has a flow capacity greater than an intakecapacity of turbine component 104 and/or first combustor 108, whichcreates an excess air flow 200. Excess air flow 200 is shown as a flowextracted from first integral compressor 106 at a discharge thereof. Itis emphasized, however, that excess air flow 200 may be extracted at anystage of integral compressor 106 where desired, e.g., at one or morelocations upstream of the discharge, at the discharge and one or morelocations upstream of the discharge, etc., using appropriate valves andrelated control systems. In any event, excess air flow 200 eventuallypasses along an excess air flow path 250, which may include one or morepipes to second turbine system(s) 140. In the FIG. 1 embodiment, acontrol valve system 202 is provided for controlling flow of excess airflow 200 to second gas turbine system(s) 140. Although illustrated as ifexcess air flow 200 is directed to just one second gas turbine system140, it is understood that the excess air flow may be directed to one ormore second gas turbine system(s) 140, where desired and where theexcess air flow can support more than one system.

Power generation system 100 may also include a turbo-expander 252operatively coupled to second turbine system 140. Turbo-expander 252 mayinclude any now known or later developed axial or centrifugal flowturbine capable of receiving a high pressure gas, such as air or steam,and generating work from the expansion of the high pressure gas. In theinstance case, at least a portion 254 of excess air flow 200 may beemployed to power turbo-expander 252. At least a portion 254 of excessair flow 200 can be augmented by another source of high pressure gas,e.g., steam from HRSG 168 and/or 170, or another pressurized air source,if necessary. Operation and advantages of turbo-expander 252 will bedescribed herein.

Excess air flow 200 can be directed from first gas turbine system 102 tosecond turbine system 140 and/or turbo-expander 252 in a number of ways.In one embodiment, a first control valve system 202 controls flow of theexcess air flow 200 along an excess air flow path 250 to at least one ofsecond gas turbine system 140 and turbo-expander 252. In terms of secondgas turbine system 140, first control valve system 202 may control flowof excess air flow 200 to at least one of a discharge 210 of secondcompressor 146, second combustor 148 and turbine nozzle cooling inlet(s)158 of second turbine component 144. Control valve system 202 mayinclude any number of valves necessary to supply the desired part ofsecond turbine system 140 with at least a portion of excess air flow200. As illustrated, control valve system 202 may include three valves.A first control valve 212 may control a first portion of excess air flow200 to discharge 210 of second compressor 146. In this fashion, excessair flow 200 can add to the flow of air from compressor 146 withoutadditional energy consumption thereby. A second control valve 214 maycontrol a second portion of excess air flow 200 to second combustor 148,thus providing additional air for combustion. A third control valve 216may control a third portion of excess air flow 200 to turbine nozzlecooling inlet(s) 158 of second turbine component 144 to provide acooling fluid for, among other things, the nozzles of the turbinecomponent. In operation the example shown may function as follows:first, with control valve 210 open and control valves 212, 214 closed,excess air flow 200 is supplied to discharge 210 of second compressor146; second, with control valves 210 and 216 closed and control valve214 open, excess air flow 200 is supplied to combustor 148; and finally,with control valves 210, 212 closed and control valve 216 open, excessair flow 200 is supplied to turbine nozzle cooling inlet(s) 158 ofsecond turbine component 144. First control valve system 202 may alsoinclude control valve 256 for controlling excess air flow 200 in excessair flow path 250. In terms of excess air flow 200 delivery toturbo-expander 252, first control valve system 202 may also include acontrol valve 266 controlling at least portion 254 of excess air flow200 supplied to turbo-expander 252 from excess air flow path 250, i.e.,to an inlet of turbo-expander 252 for powering the turbo-expander.

A second control valve system 270 may control flow of a discharge 272 ofturbo-expander 252 to an exhaust of at least one of first turbinecomponent 104 and second turbine component 144 (piping shown in dashedlines for clarity). That is, second control valve system 270 controlsflow of a portion of discharge 272 to exhaust 172 of first turbinecomponent 172 and flow of a portion of discharge 272 to exhaust 174 ofsecond turbine component 144. As illustrated, second control valvesystem 270 may include a first control valve 274 controlling a firstportion of discharge 272 of turbo-expander 252 to exhaust 172 of firstturbine component 104, and a second control valve 276 controlling asecond portion of discharge 272 of turbo-expander 252 to exhaust 174 ofsecond turbine component 144. Each portion of discharge 272 can be anypercentage of discharge 272, including zero. That is, any portion ofdischarge 272 can be delivered to first turbine component exhaust 172and second turbine component exhaust 174, or all of discharge 272 can bedelivered to exhaust 172 or exhaust 174.

With further regard to each control system 202, 270, each control valvethereof may be positioned in any position between open and closed toprovide the desired partial flows to the stated components. Further,while one passage to each component is illustrated after each controlvalve, it is emphasized that further piping and control valves may beprovided to further distribute the respective portion of excess air flow200 to various sub-parts, e.g., numerous turbine nozzle cooling inlets158 on second turbine component 144, numerous combustion cans ofcombustor 148, various inputs to turbo-expander 252, etc. As alsoillustrated, at least one sensor 220 may be provided for measuring aflow rate of at least a portion of excess air flow 200, e.g., asextracted from first integral compressor 106, after each control valve212, 214, 216, etc. Each sensor 220 may be operably coupled to controlvalve system(s) 202, 270, each which may include any now known or laterdeveloped industrial control for automated operation of the variouscontrol valves illustrated, and control system 180. Other sensors 200for measuring flow can be provided where necessary throughout powergeneration system 100.

As noted, control valve 256 may operate to control the amount of excessair flow 200 in excess air flow path 250, and a control valve 266 mayoperate to control the amount of air 254 provided to turbo-expander 252from excess air flow path 250. Control valve systems 202, 270 and henceflow of excess air flow 200 and operation of turbo-expander 252 may becontrolled using any now known or later developed industrial controller,which may be part of an overall power generation system 100 controlsystem 180. Control system 180 may control operation of all of thevarious components of power generation system 100 in a known fashion,including controlling control valve system 202.

Power generation system 100 including first gas turbine system 102having first integral compressor 106 that creates an excess air flow 200provides a number of advantages compared to conventional systems. Forexample, compressor 106 may improve the power block peak, base andhot-day output of power generation system 100 at a lower cost relativeto upgrading all compressors in the system, which can be very expensivewhere a number of gas turbines are employed. In addition embodiments ofthe invention, reduce the relative cost of an upgraded compressor, i.e.,compressor 106, and in-turn improves the viability and desirability ofan upgraded compressor by providing a way to efficiently consume more ofthe excess air flow. Further, power generation system 100 includingfirst integral compressor 106 expands the operational envelope of system100 by improving project viability in the cases where any one or more ofthe following illustrative sub-systems are undersized: turbine component104, generator 122, transformer (not shown), switchgear, HRSG 168, steamturbine system 160, steam turbine control valves, etc. In this fashion,system 100 provides an improved case to upgrade a single compressor in,for example, a two gas turbine and one steam turbine combined cycle (2×1CC) system as compared to upgrading both compressors 106, 146 or thedo-nothing case.

Turbo-expander 252 may provide a number of advantages alone or inconjunction with first integral compressor 106 that creates excess airflow 200. One advantage is that it can provide additional turning powerfor rotating shaft 152 during start up so as to augment starter motor156 power. As illustrated, second gas turbine system 140 may includerotating shaft 152 coupling second compressor 146, second turbinecomponent 144, starter motor 156 and turbo-expander 252. Generator 154may also be coupled to rotating shaft 152. Starter motor 156 may includeany now known or later developed motor for start up of second gasturbine system 140. As understood in the art, start up may includestarter motor 156 turning at a gear speed (i.e., the speed at whichrotating shaft 152 is continually turned so as to prevent bowingthereof), then increased to purge speed (i.e., speed that allows air toflow through) under influence of the motor, then reduced speed at whichcombustor 148 ignites an initial fuel flow. Subsequently, rotating shaft152 and the rest of system accelerates under influence of motor 156until it reaches full speed, no load condition (FSNL). At that point,gas turbine system 140 is not generating power, but is self-sustaining,and fuel within combustor 148 is controlling speed. Subsequently, gasturbine system 140 may be loaded (closing breaker) so it begins togenerate power using generator 154, after which adjustments such as fuelflow to combustor 148, vanes in second turbine component 144, etc., canbe made until full speed, full load (FSFL) status is attained. A similarstart up process may be employed using LCI motor 112 on first gasturbine system 102. In some instances where components of second gasturbine system 140 have been upgraded, the initial starter motor 156 maybe undersized. That is, components such as second compressor 146 and/orsecond turbine component 144 may be sized such that starter motor 156has inadequate power to function for starting up second gas turbinesystem 140. However, with the provision of turbo-expander 252 additionalturning power may be provided to rotating shaft 152 during start up soas to augment starter motor 156. In this fashion, an undersized startermotor 156 may not need to be replaced and the costs of a larger motorsuch as a load commutated inverter (LCI) motor can be avoided. (Firstgas turbine system 102 is shown with an LCI motor 112). Additionally,the torque output of turbo-expander 252 can also augment generator 154power output during periods of peak load operation where excess air flow200 supply from first compressor 106 is greater than the amount that canbe consumed by second gas turbine system(s) 140.

Another advantage of turbo-expander 252 according to embodiments of theinvention is that discharge 272 thereof has a temperature greater thanexhausts 172, 174 of first turbine component 104 and second turbinecomponent 144, respectively. Consequently, delivery of discharge 272 ofturbo-expander 252 to one or both of exhausts 172, 174, i.e., usingsecond control valve system 270, acts to heat one or more exhausts 172,174, add gas mass flow to one or more exhausts 172, 174 and increaseoutput of one or both HRSGs 168, 170 in creating steam for steam turbinesystem 160.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A power generation system, comprising: a firstgas turbine system including a first turbine component, a first integralcompressor and a first combustor to which air from the first integralcompressor and fuel are supplied, the first combustor arranged to supplyhot combustion gases to the first turbine component, and the firstintegral compressor having a flow capacity greater than an intakecapacity of at least one of the first combustor and the first turbinecomponent, creating an excess air flow, a second gas turbine systemincluding, a second turbine component, a second compressor and a secondcombustor to which air from the second compressor and fuel are supplied,the second combustor arranged to supply hot combustion gases to thesecond turbine component; a turbo-expander operatively coupled to thesecond gas turbine system; a first control valve system controlling flowof the excess air flow along an excess air flow path from the first gasturbine system to the second gas turbine system and the turbo-expander;and a second control valve system combining a flow of a discharge of theturbo-expander directly with an exhaust of the first turbine componentand the second turbine component to increase a gas mass flow of theexhaust of at least one of the first turbine component and the secondturbine component; wherein the exhaust of at least one of the firstturbine component and the second turbine component is supplied to atleast one steam generator for powering a steam turbine system.
 2. Thepower generation system of claim 1, wherein the excess air flow issupplied to a discharge of the second compressor by the first controlvalve system.
 3. The power generation system of claim 1, wherein theexcess air flow is supplied to the second combustor by the first controlvalve system.
 4. The power generation system of claim 1, wherein theexcess air flow is supplied to a turbine nozzle cooling inlet of thesecond turbine component by the first control valve system.
 5. The powergeneration system of claim 1, wherein the first control valve systemcontrols flow of the excess air flow to at least one of a discharge ofthe second compressor, the second combustor and a turbine nozzle coolinginlet of the second turbine component.
 6. The power generation system ofclaim 5, wherein the first control valve system includes a first valvecontrolling a first portion of the excess air flow to the discharge ofthe second compressor, a second valve controlling a second portion ofthe excess air flow to the second combustor, and a third valvecontrolling a third portion of the flow of the excess air flow to theturbine nozzle cooling inlets of the second turbine component.
 7. Thepower generation system of claim 6, further comprising at least onesensor for measuring a flow rate of at least a portion of the excess airflow, each of the at least one sensor operably coupled to the firstcontrol valve system.
 8. The power generation system of claim 1, whereinthe second control valve system includes a first valve controlling afirst portion of the discharge of the turbo-expander to the exhaust ofthe first turbine component and a second valve controlling a secondportion of the discharge of the turbo-expander to the exhaust of thesecond turbine component.
 9. The power generation system of claim 1,wherein the second gas turbine system further includes a rotating shaftcoupling the second compressor, the second turbine component, a startermotor and the turbo-expander.
 10. The power generation system of claim1, wherein the first gas turbine system further includes a rotatingshaft coupling the first integral compressor, the first turbinecomponent, and a load commutated inverter (LCI) motor.
 11. A powergeneration system, comprising: a first gas turbine system including afirst turbine component, a first integral compressor and a firstcombustor to which air from the first integral compressor and fuel aresupplied, the first combustor arranged to supply hot combustion gases tothe first turbine component, and the first integral compressor having aflow capacity greater than an intake capacity of at least one of thefirst combustor and the first turbine component, creating an excess airflow; a second gas turbine system including a second turbine component,a second compressor and a second combustor to which air from the secondcompressor and fuel are supplied, the second combustor arranged tosupply hot combustion gases to the second turbine component; aturbo-expander operatively coupled to the second gas turbine system; afirst control valve system controlling flow of the excess air flow alongan excess air flow path from the first gas turbine system to the secondgas turbine system and the turbo-expander; and a second control valvesystem combining a flow of a discharge of the turbo-expander directlywith an exhaust of the first turbine component and the second turbinecomponent to increase a gas mass flow of the exhaust of at least one ofthe first turbine component and the second turbine component, whereinthe second control valve system includes a first valve controlling afirst portion of the discharge of the turbo-expander to the exhaust ofthe first turbine component and a second valve controlling a secondportion of the discharge of the turbo-expander to the exhaust of thesecond turbine component, wherein the exhaust of at least one of thefirst turbine component and the second turbine component is supplied toat least one steam generator for powering a steam turbine system,wherein the second gas turbine system further includes a rotating shaftcoupling the second compressor, the second turbine component, a startermotor and the turbo-expander.
 12. The power generation system of claim11, wherein the first control valve system controls flow of the excessair flow to at least one of a discharge of the second compressor, thesecond combustor and a turbine nozzle cooling inlet of the secondturbine component.
 13. The power generation system of claim 12, whereinthe first control valve system includes a first valve controlling afirst portion of the excess air flow to the discharge of the secondcompressor, a second valve controlling a second portion of the excessair flow to the second combustor, and a third valve controlling a thirdportion of the flow of the excess air flow to the turbine nozzle coolinginlets of the second turbine component.
 14. The power generation systemof claim 11, wherein the first gas turbine system further includes arotating shaft coupling the first integral compressor, the first turbinecomponent, and a load commutated inverter (LCI) motor.